C-shaped clamp is generally used by common manufacturer for clamping two pieces of working piece, or fixing the working piece on the working table of the processing machine in order to solder, drill, lathe, grind and mill the main element of the processing work. Main structure of conventional c-shaped clamp includes a c-shaped main body and a screw which can be adjusted forward and backward, the front end of said screw possesses a movable top block, space between said top block and surface of inner side corresponding to c-shaped main body is used for accepting the working piece, and then screw is screwed to fix and clamp the working piece. If all the processed and clamped working pieces are not completely regular and plane, although the front end of screw of conventional c-shaped clamp possesses movable top block, it still can not meet the multi-use requirement of user.